A considerable amount of work has been done over the years to remove water from air, some of which have resulted in commercial success. Various reasons exist for humidity removal from ambient air, some of which include the need: a) for reducing discomfort by reduction of sensible heat; b) for maintaining commercial storage places; c) for extracting water from the atmosphere for drinking and consumption; and d) for reducing energy input for climate control units.
There are several conventional methods for removing vapor, particularly water vapor, from a gaseous stream. One method is to cool the gas stream to condense the vapor. When air is cooled below its dew point temperature, moisture condenses on the nearest surface. The process of cooling and condensation thus dehumidifies the air. Most commercial and residential air conditioning systems operate this way. Typically, a refrigeration system cools air, drains some of its moisture as condensate, and sends the drier air back to a space to be cooled. The system essentially pumps the heat from the dehumidified air to a different air system in another location, by using refrigerated gas to carry the heat.
Another method is to contact the gaseous stream with a desiccant capable of pulling water vapor out of the gas stream by a difference in vapor pressures. Desiccant dehumidifiers, instead of cooling the air to condense moisture, attract moisture from the air by creating an area of low vapor pressure at the surface of the desiccant. The pressure exerted by the vapor in the air is higher, so the vapor molecules move from the air to the desiccant, which is typically a layered, hydrophilic alumina silicate matrix that can tie up “liquid” phase water, resulting in dehumidifying the air. Hence, for a desiccant to work, there must be a phase change of the water. Desiccant dehumidifiers make use of changing vapor pressures relative to dry air in a repeating cycle.
While the above methods have met with commercial success, they unfortunately require large amounts of energy to extract the latent heat of water from air, thus hardly making a difference in reducing the load on the cooling requirement of an air conditioning unit. Therefore, there remains a need in the art for the extraction of water from ambient air in a more energy efficient manner.